|Publication number||US8143687 B2|
|Application number||US 12/640,586|
|Publication date||Mar 27, 2012|
|Filing date||Dec 17, 2009|
|Priority date||Dec 17, 2009|
|Also published as||EP2337082A2, US20110147877|
|Publication number||12640586, 640586, US 8143687 B2, US 8143687B2, US-B2-8143687, US8143687 B2, US8143687B2|
|Inventors||Justin G. A. Wehner, Scott M. Johnson|
|Original Assignee||Raytheon Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Non-Patent Citations (1), Referenced by (1), Classifications (19), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates generally to radiation detectors, and more particularly to multi-band, reduced-volume radiation detectors and methods of formation.
Infrared detectors are used in a variety of applications. For example, some infrared detectors are used in the military field, remote sensing, and infrared astronomy research. Infrared detectors are negatively affected by a variety of noise sources. Moreover, some infrared detectors are cooled to operating temperatures near or below that of liquid nitrogen (77K) to reduce noise, such as, noise caused by thermally excited current carriers.
Broadband radiation detectors and methods of forming the same are disclosed. According to one embodiment, a broadband radiation detector includes a first layer having a first electrical conductivity type. A second layer has a second electrical conductivity type and an energy bandgap responsive to radiation in a first spectral region. A third layer has approximately the second electrical conductivity type and an energy bandgap responsive to radiation in a second spectral region of longer wavelength than the first spectral region. The broadband radiation detector further includes a plurality of internal regions. In certain embodiments, each internal region may be disposed at least partially within the third layer. Each of the plurality of internal regions may include a dielectric constant that is different from a dielectric constant of the third layer. In particular embodiments, each of the plurality of internal regions comprises one or more of an organic polymer, a silicon compound, and an air gap. In various embodiments, the plurality of internal regions may be arranged according to a regularly repeating pattern.
In a method embodiment, a method of forming a broadband radiation detector includes forming a first layer having a first electrical conductivity type. The method further includes forming a second layer having a second electrical conductivity type and an energy bandgap responsive to radiation in a first spectral region. The method also includes forming a third layer having approximately the second electrical conductivity type and an energy bandgap responsive to radiation in a second spectral region. In this particular embodiment, the second spectral region comprises at least one wavelength that is longer than a wavelength in the first spectral region. The method includes, selectively removing portions of the third layer. In this example, the portions selectively removed from the third layer are arranged with respect to each other according to a regularly repeating pattern. The method also includes, partially filling each of the portions selectively removed from the third layer with a passivation layer having a refractive index that is substantially different from a refractive index of the third layer.
Particular embodiments disclosed herein may provide one or more technical advantages. For example, various embodiments may be capable of providing clear image, broadband infrared detection due at least in part to enhanced noise mitigation. Particular embodiments may be capable of broadband infrared detection at operational temperatures at or below that of liquid nitrogen (approximately 77 Kelvin) and up to a desired operating temperature, such as, for example an operating temperature within the range of approximately 200 to 250 Kelvin. Certain embodiments may provide enhanced performance within the various spectral regions. Certain embodiments may provide all, some, or none of these advantages. Certain embodiments may provide one or more other advantages, one or more of which may be apparent to those skilled in the art from the figures, descriptions, and claims included herein.
For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:
Various example embodiments disclosed herein are explained in the context of radiation detectors and methods of formation. Certain embodiments may provide enhanced performance within multiple infrared spectral regions. Various embodiments may be capable of providing broadband infrared detection at higher operating temperatures due at least in part to enhanced noise mitigation. As explained further below, particular embodiments may provide noise mitigation at least in part by volume reduction of noisier bandgap regions within the infrared detectors. Although various example embodiments disclosed herein are explained in the context of multi-band, reduced-volume, infrared detectors and methods of formation, the teachings of the present disclosure could be applied to any of a variety of alternative radiation detectors including, for example, photodiodes, photoconductive detectors, photovoltaic detectors, photodiode detectors, or any other suitable radiation detector responsive to a variety of different spectral regions. Additionally, particular embodiments disclosed herein may be implemented using any number of techniques, whether currently known or in existence. The present disclosure should in no way be limited to the example implementations, detector materials, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale.
In particular embodiments, semiconductor layers 106, 108, and/or 110 may be formed by epitaxy. For example, molecular beam epitaxy may be used to enable a stack of semiconductor layers 106, 108, and/or 110 having different alloy compositions. The varying alloy compositions may allow simultaneous radiation detection at multiple spectral regions. In addition, molecular beam epitaxy may allow growth on large area substrates. Although particular embodiments are explained in the context of molecular beam epitaxy, any suitable processing techniques, including future processing techniques, may be used to form semiconductor layers 106, 108, and/or 110 outwardly from substrate 104. For example, in alternative embodiments a metalorganic vapor phase epitaxy and/or a liquid phase epitaxy may be used.
At least two of the semiconductor layers 106, 108, and 110 may comprise material having energy bandgaps responsive to radiation in respective spectral regions. In a particular embodiment, semiconductor layer 106 may have an energy bandgap responsive to a spectral ranger of approximately 5 microns to 0.5 micrometers, and semiconductor layer 110 may have an energy bandgap responsive to a different spectral region, such as, for example, long-wavelength infrared (LWIR). In alternative embodiments, semiconductor layers 106, 108, and/or 110 may be responsive to respective ones or more of near-infrared (NIR), short-wavelength infrared (SWIR), mid-wavelength infrared, LWIR, very-long wave infrared (VLWIR), and/or one or more other spectral regions that may or may not be within the infrared spectrum. As used herein, NIR radiation includes a spectral region extending from approximately 0.5 to 1 micrometers, SWIR radiation includes a spectral region extending from approximately 1 to 3 micrometers, MWIR radiation includes a spectral region extending from approximately 3 to 8 micrometers, LWIR radiation includes a spectral region extending from approximately 8 to 12 micrometers, and VLWIR radiation includes a spectral region extending from approximately 12 to 30 micrometers.
One example material capable of detecting radiation is mercury cadmium telluride (HgCdTe). In a particular embodiment, semiconductor layers 106, 108, and/or 110 at least partially comprises HgCdTe in the form of Hg(1-x)CdxTe. The x value of the HgCdTe alloy composition may be chosen, for example, so as to tune the optical absorption of the corresponding semiconductor layer 106, 108, and/or 110 to the desired infrared wavelength. In a particular embodiment, layer 106 may be comprised of Hg0.55Cd0.45Te and layer 108 may be comprised of Hg0.7Cd0.3Te; however, the x of Hg(1.0-x)CdxTe for layers 106, 108, and/or 110 may be any suitable value depending, for example, on the desired range of optical absorption. In alternative embodiments, layers 106, 108, and/or 110 may comprise additional and/or alternative materials responsive to radiation. For example, layers 106, 108, and/or 110 may comprise mercury cadmium zinc telluride (HgCdZnTe) and/or III-V semiconductor materials, such as, for example, GaAs, AlGaAs, InAs, InSb, GaSb, and their alloys. As another example layers 106, 108, and/or 110 may be based on a type-II strained-layer superlattice structure.
In various embodiments, semiconductor layers 106, 108, and/or 110 may have respective types of electrical conductivity. For example, semiconductor layers 106 and 110 may each be n-type and semiconductor layer 108 may be p-type, thereby creating an n-p-n polarity. As another example, semiconductor layers 106 and 110 may be p-type and semiconductor layer 108 may be n-type, thereby creating a p-n-p polarity. A variety of other suitable electrical conductivity variations may be used for semiconductor layers 106, 108, and/or 110 including, for example, combinations that include additional or fewer semiconductor layers. Referring to the alternative embodiment illustrated in
In step 204, internal regions 112 are formed within one or more of semiconductor layers 106, 108, and/or 110 at least in part by reducing the volume of the corresponding layer or layers. For example, portions of semiconductor layer 106, 108, and/or 110 may be selectively removed. In a particular embodiment, the portions may be selectively removed by photolithography and etching; however, any suitable volume reduction process or combination of processes may be used. The volume reduction of semiconductor layers 106, 108, and/or 110 may be configured in a periodic pattern designed to affect the motions of photons through the corresponding semiconductor layers 108, 108, and/or 110. In this manner, internal regions 112 may be capable of causing a resonant effect upon the particular semiconductor layers 106, 108, and/or 110 within which internal regions 112 may be disposed. Thus, even though volume may be removed from one or more photon detecting regions of semiconductor layers 106, 108, and/or 110, these reduced-volume regions may still be capable of resonating in such a way as to absorb sufficient photons in the active material for accurate radiation detection.
In various embodiments, internal regions 112 may each generally extend along an axis substantially perpendicular to one or more planar surfaces of semiconductor layers 106, 108, and/or 110. As shown in
In various embodiments, internal regions 112 may be disposed at least within the semiconductor layer 106, 108, and/or 110 having the longest wavelength bandgap absorption of the semiconductor stack 106, 108, and 110. Accordingly, formation of internal regions 112 within each detector 102 of FPA 100 may, in certain cases, result in volume reduction of the longest wavelength band absorption region of FPA 100. The volume reduction of this longest wavelength band absorption region may provide a number of advantages. For example, reducing the volume of the longest wavelength band absorption region may reduce a variety of noises that might otherwise be generated by this region. In particular, noise due to diffusion and generation-recombination currents, or diffusion and g-r noise, may be types of electrical signal noise that may be reduced by internal regions 112. Additionally, 1/f noise sources may be reduced by the volume reduction achieved by internal regions 112. The term 1/f noise as used herein generally refers to any noise with a power spectral density of the form S(f)∝1/fα, where f is frequency and 0<α<2, with a usually close to 1. A variety of other types of noises associated with conventional infrared detectors may also be mitigated by the formation of internal regions 112 within the longest wavelength band absorption region of FPA 100.
In certain embodiments, the volume reduction of semiconductor layers 106, 108, and/or 110 may result in an increased surface area and an increased surface-to-volume ratio of the volume-reduced semiconductor layers 106, 108, and/or 110. The increased surface area and surface-to-volume ratio may compound the risk of recombination and/or carrier loss, potentially resulting in high noise current and a variety of other issues.
In step 206, passivation layer 114 is formed outwardly from portions of FPA 100. As shown in
In step 208, internal regions 112 may be wholly or partially back-filled. For example, the remainder of the voids of each internal region 112 may be at least partially filled. In particular embodiments, the void-filling material or materials may have respective refractive indices that differ from respective refractive indices of the particular semiconductor layers 106, 108, and/or 110 within which internal regions 112 may be disposed. For example, as mentioned previously with reference to step 206, the voids may be wholly or partially filled by passivation layer 114. Additionally or alternatively, the voids may be wholly or partially filled by one or more other layers, such as, for example, an organic polymer (e.g., photoresist), an oxide (e.g., silicon dioxide), a nitride (e.g., silicon nitride), and/or any other suitable filler layer. In various embodiments, all of or a portion of the voids may remain unfilled, leaving an air gap disposed within internal regions 112. In another embodiment, each void may at least partially define an enclosed area filled with one or more gases and/or substantially free of matter (e.g., a vacuum). In certain embodiments, wholly or partially filled internal regions 112 may have refractive indices and/or the dielectric constants differing from that of the refractive indices and/or dielectric constants of the particular semiconductor layers 106, 108, and/or 110 within which internal regions 112 may be disposed. These differences in refractive indices and/or dielectric constants may, in certain cases, have a beneficial resonant effect upon photons moving through semiconductor layers 106, 108, and/or 110.
In step 210, the outmost surface of the semiconductor layer stack may be planarized. As shown in
In step 212, a respective contact 116 is formed outwardly from each infrared detector 102. In particular embodiments, each contact 116 may enable the corresponding infrared detector 112 to electrically communicate a signal to readout circuitry, as explained further below with reference to
In operation, at least two of semiconductor layers 106, 108, and/or 110 may be capable of radiation detection when a photon of sufficient energy kicks an electron from the valence band to the conduction band within one of these layers. Such an electron is collected by a suitable external readout integrated circuits (ROIC) and transformed into an electric signal. In particular embodiments, FPA 100 may also refer to and include the physical mating of the detector array to the ROIC, as explained further with reference to
In a particular embodiment, layers 306 and 310 may be n-type layers substantially similar in structure and function to various embodiments of semiconductor layers 106 and 110, respectively, and layer 308 may be a p-type capping layer substantially similar in structure and function to various embodiments of semiconductor layer 108. Thus, the semiconductor stack may, in certain embodiments, include an n-type semiconductor layer 310 disposed between another n-type semiconductor layer 306 and a p-type semiconductor layer 308. In certain embodiments, internal regions 312, layer 314, and contact 316, may be substantially similar in structure and function to internal regions 112, passivation layer 114, and contact 316, respectively, of
Accordingly, particular embodiments may be capable of broadband radiation detection. In certain embodiments, two different regions of a radiation detector may have respective, differing bandgaps. The volume of the noiser bandgap region may be reduced, thereby potentially reducing the noise contribution of the dominant noise source. In some embodiments, the volume of other regions may also be reduced, even though such regions may or may not be a diffusion noise source. For example, FPAs 100 and 300 both illustrate volume reduction of layers 108 and 308, though such layers may or may not be a diffusion noise source. Even though material of an absorption region may be removed in some embodiments, detector performance may be maintained, or even improved in some cases, by the inclusion of a pattern of internal regions 112 that affect the resonance of the volume-reduced absorption region. In particular embodiments, a photonic crystal pattern may be used for the internal regions 112. In addition to potential noise reduction, various radiation detectors may be functional at higher operational temperatures than the operational temperature ranges of conventional infrared detectors. As disclosed above, particular embodiments may be capable of broadband infrared detection at an operating temperature within the range of approximately 200 to 250 Kelvin, depending on the wavelength of detection.
The components of the systems and apparatuses disclosed herein may be integrated or separated. Moreover, the functions of the elements and/or layers may be performed by more, fewer, or other components. For example, particular embodiments may include one or more filtering layers and/or one or more diffraction gratings. As another example, particular embodiments may include only two semiconductor layers. The methods may include more, fewer, or other steps. For example, steps 206 and 208 may be combined in a single step that includes the formation of passivation layer 114 within internal regions 112. Additionally, steps may be performed in any suitable order. Particular operations of the systems and apparatuses disclosed herein may be performed using any suitable logic embodied in computer-readable media. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
Although the present disclosure has been described above in connection with several embodiments, a myriad of changes, substitutions, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, substitutions, variations, alterations, transformations, and modifications as fall within the spirit and scope of the appended claims. For example, in various alternative embodiments one or more infrared detectors may be formed be reducing the volumes of multiple semiconductor layers, such that a pattern of pillars substantially similar in dimensions to internal regions 112 remain and such that the semiconductor volume surrounding the pillars is selectively removed. The pillars may have a configuration substantially similar to a photonic crystal pattern. In certain embodiments, the pillars may be wholly or partially encased by one or more outwardly disposed layers, such as, for example, one or more passivation layers.
To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3971065||Mar 5, 1975||Jul 20, 1976||Eastman Kodak Company||Color imaging array|
|US4783594||Nov 20, 1987||Nov 8, 1988||Santa Barbara Research Center||Reticular detector array|
|US5113076||Dec 19, 1989||May 12, 1992||Santa Barbara Research Center||Two terminal multi-band infrared radiation detector|
|US5559336||Jul 5, 1994||Sep 24, 1996||Santa Barbara Research Center||Integrated LPE-grown structure for simultaneous detection of infrared radiation in two bands|
|US5731621||Mar 19, 1996||Mar 24, 1998||Santa Barbara Research Center||Three band and four band multispectral structures having two simultaneous signal outputs|
|US5959339||Mar 19, 1996||Sep 28, 1999||Raytheon Company||Simultaneous two-wavelength p-n-p-n Infrared detector|
|US6049116||May 13, 1998||Apr 11, 2000||Agency For Defense Development||Two-color infrared detector and fabrication method thereof|
|US7135698||Dec 5, 2002||Nov 14, 2006||Lockheed Martin Corporation||Multi-spectral infrared super-pixel photodetector and imager|
|US7145124 *||Sep 15, 2004||Dec 5, 2006||Raytheon Company||Multispectral imaging chip using photonic crystals|
|US20070145273||Dec 22, 2005||Jun 28, 2007||Chang Edward T||High-sensitivity infrared color camera|
|1||Krishna, et al., "Quantum Dot Infrared Sensors with Photonic Crystal Cavity," Proceedings of the Laser and Electro-optical Society, vol. 1, pp. 909-910, Dec. 5, 2005.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8941203||Sep 12, 2012||Jan 27, 2015||Raytheon Company||Photodetector with surface plasmon resonance|
|U.S. Classification||257/446, 438/73, 257/461, 257/E31.093, 257/465, 257/E31.039, 257/448, 257/E27.143, 438/81|
|Cooperative Classification||H01L27/14683, H01L31/0232, H01L31/101, H01L31/035272, H01L27/1446|
|European Classification||H01L31/101, H01L27/144R, H01L31/0352C, H01L31/0232|
|Dec 17, 2009||AS||Assignment|
Owner name: RAYTHEON COMPANY, MASSACHUSETTS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:WEHNER, JUSTIN G. A.;JOHNSON, SCOTT M.;SIGNING DATES FROM 20091214 TO 20091216;REEL/FRAME:023670/0193
|Sep 9, 2015||FPAY||Fee payment|
Year of fee payment: 4